3D time-of-flight (TOP) cameras are active optical depth measurement systems. In general, TOF systems are based on the phase-measurement technique of emitted intensity-modulated light, which is reflected by the scene. The reflected light is imaged onto a sensor. The photo-generated electrons are demodulated in the sensor. Based on the phase information, the distance for each pixel is deduced. A more detailed description is presented by Oggier et al. in “An all-solid-state optical range camera for 3D real-time imaging with sub-centimeter depth resolution (SwissRanger)”, Proc. Of the SPIE, Vol. 5249, pp. 534-545, 2004.